Dimming LV downlighters

[petek]

I have just had some wardrobes fitted either side of the bed with top boxes above. Under the top boxes there are 2 low voltage downlighters fitted with electronic transformers. At my request the wardrobe fitters have left the lights for me to connect up because I want to fit 2 dimmer switches either side of the bed, so that the 2 downlighters can be controlled separately.

Have just bought 2 "Varilight" dimmer switches from B&Q but the instructions say they are only suitable for a minimum load of 100W otherwise the dim function will not work succesfully.

Has anybody any experience of this?

Are there special dimmer switches available for controlling just one LV downlight, if so, where from?

I was intending to fit the dimmer in the mains side of the transformer but perhaps there are dimmer switches available to fit in the LV side?

TIA Pete

[fred]

In article , petek writes

IQ dimmers from TLC have a lower minimum of 40W but it's certainly not uncommon to have a minimum for correct operation. Would 2x20W lamps suit your usage?

the minimum I quoted was for the touch/remote dimmers but I have assumed the knob type will be similar, they are certainly the type they recommend for LV lighting. In my limited experience I have not seen dimmers on the LV side.

[Owain]

Yes. 'Tis true, I'm afraid.

Why not add some upward facing downlighters in the top of the top boxes to bounce some light off the ceiling and take you above the dimmers' min rating?

I'd be inclined to go with bounced light anyway, no way would I want to lie back in bed and have halogens glaring in my face.

Owain

[John Rumm]

Yup, found the same with a 250W transformer freeding a 4 lamp track light. It needs three or more 50W bulbs in there to get sensible operation from the dimmer.

[meow2222]

i assume you realise that most electronic transformers wont run correctly off a dimmer. And that dimming halogens is very energy inefficient, you lose a lot of light for a little energy reduction. A switchbank is usually much better, though it sounds like you may not have laid the lighting out to suit.

NT

[Andrew Gabriel]

All the ones I've bought in the last 10 years explicitly state they will run off dimmers (although I don't).

[petek]

Thanks to all for the replies, I am now a little wiser! The TLC site was most useful (thanks Fred) where I found a Low Voltage Dimmer (their ref VL CP401) which it states is suitable for electronic transformers. Unfortunately the spec. didn't state a minimum wattage, but an e-mail to the TLC technical helpdesk was replied to very quickly stating 40W minimum. This is fine for me so I've ordered 2 of them.

I take the point about halogens glaring in my face (our faces) and also about inefficiency, but will have to wait and see what they are like when I've got them wired up.

[unopened]

Using a gold-plated sledgehammer to crack a nut here, wouldn't just putting a variac (autotransformer) in front of the transformer work? The OP probably wouldn't want to do this, looking at the price of the things, but shouldn't that work, no matter what the AC-to LV DC transformer is: a lump or a switched mode?

Not having done this myself, won't running the halogen lamp at lower than design voltage shorten it's life? I thought they relied on the halide cycle to control the evaporation of the filament, and if kept dim, this doesn't work, drastically reducing the life of the lamp.

Sid

[stopbox]

This is changing as specifications for transformers have improved without costing as much as they used to. We sell our downlights bundled with Tridonic Speedy electronic transformers that can be used with either leading edge or trailing edge dimmers to offer step-less dimming.

The built-in electronic filter circuits and phase rounding circuits eliminate the problems associated with dimming low voltage downlights.

High specification dimmers like these have dropped in price over the last few years and we bundle them with a cast fixed downlight and Osram build for £7.95 (inc VAT).

Regards - Jack